1. Field of the Invention
The present invention relates to a slot antenna, and more specifically to a slot antenna having slots formed on both sides of a dielectric substrate.
2. Discussion of Related Art
In recent, as information and communication technologies developed rapidly, the radio communication system has been developed to transmit various wideband data such as multimedia data differently from the conventional radio communication system for transmitting only voice. A radio communication terminal used in a radio communication system becomes compact and lightweight as portability of the radio communication is important.
Accordingly, wide band, compact, and lightweight antenna used in the radio communication terminal will be required. Normally, a microstrip patch antenna is used as a compact and lightweight antenna. However, there is a problem that a frequency bandwidth of the microstrip patch antenna is very narrow. On the other hands, the slot antenna has relatively wide frequency bandwidth and low cross polarization level characteristics.
Now, the conventional slot antenna will be described with reference to accompanying drawings.
FIG. 1A is a view showing a basic structure of the conventional slot antenna. The slot antenna in FIG. 1A comprises a dielectric substrate 11 having a predetermined dielectric constant and thickness, a slot 12 having a length of ½ center frequency wavelength λ on one surface of the dielectric substrate, and a microstrip feed line 13 for supplying electromagnetic field energy to the slot 12 formed on the other surface of the dielectric substrate. Reference numeral 14 indicates a ground surface formed on the one surface of the dielectric substrate 11.
FIG. 1B is a view showing an electric field distribution generated by the electric field energy, which is supplied to the slot 12 through the microstrip feed line 13. The electromagnetic field is radiated into free space through the generated electrical field. This slot antenna has relatively wide frequency bandwidth characteristics. However, since a slot having a λ/2 length should be formed on the antenna, there is a problem that the slot antenna becomes large.
Accordingly, in the art, a meandered slot antenna has a structure capable of reducing a size of the antenna by forming the slot in the antenna to have a horizontally bended form in order to reduce a size of the conventional slot antenna. The meandered slot antenna structure was disclosed in Microwave and Optical Tech Letters, vol. 24, pp. 377–380, 2000, entitled “compact Meander Slot Antennas,” written by H. Y. Wang, J. Simkin, and Jung-Min Kim, Jong-Gwan Yook, “compact Meander-Type Slot Antennas,” and Antennas and Propagation Society, 2001 IEEE International Sym., vol. 2, pp. 724–727, 2001″.
FIG. 2A is a view showing a basic structure of the conventional meandered slot antenna. The meandered slot antenna comprises a dielectric substrate 21, a slot 22 formed on one surface of the dielectric substrate, and a microstrip feed line 23 formed on the other surface of the dielectric substrate to supply electromagnetic field energy to the slot 22. The slot 22 is horizontally formed to have a “” shape, that is, a meandered shape on one surface of the dielectric substrate 21. The slot antenna having a length of ½ center frequency wavelength is gradually decreased in size depending on the bending number of the slot. Reference numeral 24 indicates a ground surface formed on the one surface of the dielectric substrate 21.
The electric field distribution of the slot antenna having the slot 22 of the meandered structure is shown in FIG. 2B. In the slot 22 in FIG. 2B, an electric field component A and an electric field component B are arranged in parallel and in opposite directions to be counterbalanced, thereby reducing the electromagnetic energy radiated from the slot.
Accordingly, a gain and a radiation efficiency of the meandered slot antenna, defined by an equation (1) and (2), are very low.Gain=4π(Radiation strength/Antenna input power)  (1)Radiation efficiency=(Radiation power/Antenna input power)  (2)
As shown in the equations 1 and 2, the gain and the radiation efficiency of the antenna are indexes representing magnitude of the radiated energy with the exception of energy lost by loss factors of dielectric or conductor of the antenna or energy lost around the periphery of the antenna as a reactance component. It means that if the gain and the radiation efficiency of the antenna are increased, energy radiated from the antenna is also increased.
FIG. 3 is a view showing dimensions of the slot antenna and the meandered slot antenna used in a simulation test for monitoring decrement in the gain and the radiation efficiency according to a meandered structure of the slot. A width of the slot is 0.3 mm. In this case, the gain and the efficient of the antennas are represented in table 1. At that time, the used substrate has characteristics, such as a thickness of 100 μm, a permittivity of 12.9, a loss tangent of 0.002, and a center frequency of 5.775 GHz. As shown in table 1, it is understood that the gain and the radiation efficiency of the antenna are decreased by 6 dBi and 30% respectively when the meandered structure is used in the slot.
TABLE 1SLOTMEANDERED SLOTANTENNAANTENNA10 dB FREQUENCY BAND30.040.0WIDTH (MHz)ANTENNA GAIN(dBi)−1.0−7.0ANTENNA RADIATION40.010.0EFFICIENCY (%)
Accordingly, since the conventional slot antennas still cannot concurrently satisfy both characteristics, that is, gain and radiation efficiency characteristics and compact and lightweight characteristics, it is fully necessary to develop a new shaped slot antenna.